<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <style>
        body {
          margin: 0;
        }

        .box {
          position: absolute;
          left: 50px;
          top: 50px;
          width: 50px;
          height: 50px;
          background: green;
        }
        </style>

<div class="box"></div>
